Three major sectors of the American economy—industrial, residential, and commercial—are ripe for tremendous energy savings. McKinsey & Company estimates that by 2020, capturing the economy’s full efficiency potential will save $442 billion in energy costs and 300 megatons of CO2e in the industrial sector; $395 billion and 360 megatons of CO2e in the residential sector; and $290 billion and 360 megatons of CO2e in the commercial sector. The total possible savings in energy costs and greenhouse gas emissions are staggering: more than $1.1 trillion and 1,020 megatons of CO2e by the end of this decade.